Oil permeable steel and method for manufacturing the same



U td W m on. rERMEABLE STEEL fmrr on FORT MANUFACTURING SAME 5020 Kawasaki, Minatoku, Tokyo, Japan No Dra ing.- enpl tati u No mber 22,19

Ser a N9. 5 .48465 .v

' the like. This invention has as its object to provide an oil permeable steel of high tensile strength. In this invention, for this object, steel is expanded by repeated heating to a required degree and permitting it to cool to produce growth of the steel so that its increased porosity results in increased permeability of the steel by lubricants. This oil permeable grown steel is adapted to be utilized effectively as sliding parts of machines including bearings, piston rings, cylinder liners, etc., and jigs for making machine parts.

It is already known that cast iron grows due to the presence of its free graphite content, when it is subjected to repeated heating and cooling above and below its A transformation.

The process of growing cast iron to produce oil permeable cast iron, is disclosed in U.S. application Serial Number 344,891, filed on March 26, 1955, by the instant inventor, now U.S. Patent 2,763,583, issued September 18, 1956.

Since an ordinary steel does not grow into porous steel, in the absence of free graphite in its matrix, even when subjected to repeated heating and cooling above and below its A, transformation, porosity can never be produced. When steel, having been previously subjected to special heat treatment (that is, high temperature annealing), is graphitized into so-called graphitic stee I have discovered that its porosity increases when it is subjected to repeated heating and cooling above and below its A, transformation similar to the case with cast iron.

The graphitization of steel after high temperature annealing has been prior disclosed in the following publications:

(1) F. R. Bont & Mertin Fleshman: Metal Progress, 1937, p. 409.

(2) A. B. Wilder, T. 0. Tyson: Trans. A.S.M., 1948, p. 233.

(3) A. F. Sprankle: Iron Age, 1952, p. 108.

All of these relate to graphitic steel after high temperature annealing, which improves antiwear characteristics for lubricating behaviour of its free graphite and has been utilized as dies or the like. In accordance with my discovery, my instant invention is directed to the method or providing porosity, as the result of growth, to graphitic steels. Thus, by way of example, one steel that I used in my investigations had the following components and mechanical properties: C, 1.6%; Si, 1%; Mn, 0.12%; P, 0.24%; remainder Fe. Tensile strength, 80 kg./mm. Shore hardness, 52; specific gravity, 7.7; impact value (Izod), 9.

The above mentioned steel is kept heated at 900 C. for 20 hours and then cooled in furnace down to 400 C. at a cooling speed of 25 C./hour, and again kept heated at 750 C. for 25 hours and again cooled in furnace down to 400 C. at cooling speed of 60 C./hour. As a result,

some of the carbon .in the steel steel grows into graphitic steel.

Then is teel i s bj cted to sustained heating at approximately 750 C. to 850 Cu ma tis, above its A tr formatio p i t, f r 1.5. hours andis ooled-in air down to 400 C. a a c ling speed of 0 .C/hour. A ter o y ep i n of this .h at'tre tm ntflc nnect 5 c a ks are Prod ced a h gr n boundaries itlte' Precipitated phite, that is. it grows, "This grown steel. thus. obtained. sho s the tcllaw ng mechanical prope ie T le stre g h. 0 lie/intu S ardness, 35; are cific g a ity. ;-1 .mpat a1 l. 5

Finally i ro n s e 'is. .permeat dwi h mach e. at at c. for Q e-hear oi bath with a resu t tat-fit as, 5% f oil en by qlu ne- Grown steel obtained in accordance with this invention has approximately five times the;medhttnical-strengthatid approximately six times the ductility in comparison with an ordinary grown cast iron, of which latter the mechanical strength is 13-15 kg./mm. Steel treated according to my instant invention is very superior in every respect for heavily loaded machine elements involving sliding action such as, for example, bearings, piston rings and cylinder liners. As for the raw materials of grown steel, the situation is pretty much the same as in the case of gray cast iron; the silicon content of graphitic steel is a decisive factor in the precipitation of free graphite and at the same time the annealing temperature is more or less influenced by the silicon content. From various experiments which have been performed, it is concluded that graphitization in steel of 1.5% C occurs respectively for 0.5% Si at 970 to 1100 C., for 0.5% Si to 1% Si at 700 C. to 950 C., and for 1% Si to 2% Si at 650 C. to 700 C. For more than 2% Si, graphitization is further promoted, but is liable to produce serious cracks, eventuating in degeneration of its mechanical properties. Therefore a proper silicon content is 1% to 2% for approximately 1.5% C steel.

Further, in order to improve mechanical properties, other metals should be added adequately, for example, Ni (no more than 2%), Cr (no more than 1%), W (no more than 3%), Mo (no more than 0.6%) and Mn (no more than 1%).

I claim:

1. The method of producing oil permeable porous carbon steel comprising the steps of heating steel containing from 1.5% to 1.6% carbon and from 0.5% to 2.0% silicon and the balance substantially iron a first time to a temperature in the range of 650 C. to 1100" C. in inverse relationship to the silicon content for a period of about twenty hours and permitting the steel to cool in the furnace at a rate of about 25 C. per hour to about prec pita ed and the 400 C., heating the steel a second time to a temperature of about 750 C. for about twenty-five hours and permitting it to cool at a rate of about 60 C. per hour to about 400 C., subjecting the steel to a third heating to about 750 C. to 850 C. for a period relatively short as compared to each the period of the first and the second heatings and permitting it to cool at a rate of about 50 C. per hour comparable to the second controlled rate, and repeating the third heating and cooling for a total of about forty times.

2. The method according to claim 1 in which the steel contains substantially 1.5% carbon and substantially 0.5% silicon and the first heating is to a temperature in the range from 970 C. to 1100 C.

3. The method according to claim 1 in which the steel contains substantially 1.5% carbon and from 0.5% to 1.0% silicon and the first heating is to a temperature of from 700' C. to 950 C.

4. The method according to claim 1 in which the steel contains substantially 1.5% carbon and from 1% to 2% silicon and the first heating is to a temperature of from 650 C. to 700 C.

5. The method according to claim 1 in which the steel. contains about 1.6% carbon, 1% silicon, 0.12% manganese and 0.024% phosphorous and in which the first heating is .to a temperature of about 900 C., and the period for which the temperature of the third heatings is maintained is one and one-half hours.

,6. The method according to claim 1 in which the carbon steel contains in addition at least one component selected from the group consisting of up to 2% nickel, up to 1% chromium, up to 3% tungsten, up to 0.6% molybdenum and up to 1% manganese. f 7. As a new article of'manufacture, a carbon-silicon steel defining oil permeable. interconnected surface and body interior microscopic voids and having a composition of from 1.5% to 1.6% carbon and from 0.5% to 2.0% silicon and the remainder substantially iron.

8. As a new article of manufacture, a carbon-silicon steel defining oil permeable interconnected surface and body ,-interior microscopic voids and having a composi- ,892,745 n A m tion of about 1.6% carbon, about 1% silicon, about 0.12% manganese, about 0.024% phosphorous, and the remainder iron.

9. As a new article of manufacture, a carbon-silicon steel defining oil permeable interconnected surface and body interior microscopic voids and having a composition of from 1.5% to 1.6% carbon, from 0.5% to 2.0% silicon, at least one component selected from the group con'sistingof up to 2% nickel, up to 1% chromium, up to 3% tungsten, up to 0.6% molybdenum and up to 1% manganese, and the remainder substantially iron.

References Cited in the file of this patent UNITED STATES PATENTS Pack Oct. 7, 1924 Bont Dec. 31, 1946 OTHER REFERENCES Bont et aL: 409-413. 

